Within the area of engine control systems, it is desirable to avoid the phenomenon known as knock to optimize the performance of the engine and to avoid damages on the engine. In order to control the operation of the engine and avoid knock while at the same time optimize the operation, maps (i.e. tables of data) are commonly used. A map may be a table of values for a particular parameter at different operating conditions of the engine (e.g., a particular speed and load). These parameters are typically predetermined for a specific engine. It is also known to use data regarding the ion current to detect knock or calculate knock index. A generation of a knock event in an engine is a considerable problem, because when an engine knocks it can also cause severe damages on the engine. In an internal combustion engine the air and fuel mixture is introduced into a combustion chamber and then compressed by an ascending movement of a piston, the compressed mixture is fired and combusted by a spark that is generated by applying a high voltage to a spark plug installed in the combustion chamber and the force produced as the piston is pushed down is recovered as work. Occasionally the pressure created by the combustion itself can cause the air and fuel mixture not yet combusted to ignite prematurely, creating a smaller, instantaneous combustion of the end gas that is the cause of the knock event. This condition is not desirable because it can damage or destroy engine parts so it is desirable to prevent the generation of knock event. When combustion is performed in the combustion chamber, molecules of the mixture in the chamber are ionized, so when a measuring voltage is impressed to the spark plug in the combustion chamber, a current, ion current, flows due to the electric charge of the ions. It is known that the ion current changes depending on the combustion pressure and hence, occurrence of a knock (pressure oscillation) can be determined by detecting the signal content of the ion current.
Performance of an engine may be affected by a variety of environmental factors—fuel quality, humidity, air quality, oil quality, air temperature, and the like. An engine should be adaptable to different fuel sources (e.g., different ethanol or methanol concentrations in gasoline, different biodiesel concentrations in diesel, and/or different natural gas components). Additionally, many engines are designed for multi-fuel use (e.g., using diesel and natural gas). Within these categories, fuel quality may vary (e.g. the concentration of sulfur, water, and/or other contaminants). Different fuels may have different energy content. Therefore different fuels may result in significantly different in cylinder pressure for the same amount of combusted fresh air mixed with the fuel to achieve a given (e.g., stoichiometric) combustion.
Engine load is often estimated using an air mass flow sensor. Under the assumption of a known fuel energy content an estimate of the engine load can be computed. Once the engine load has been estimated it is straight forward to compute the corresponding in cylinder pressure. However, if the energy content of the fuel varies, the computed in cylinder pressure may be incorrect. This may degrade the engine performance and/or damage the engine.
There is a need to find a solution to the above mentioned problems to optimize engine work and suppress knocks.
U.S. Pat. No. 6,748,922 B2 discloses a knock control apparatus for internal combustion engines, the knock control apparatus comprises a frequency magnitude calculation part that includes a frequency magnitude detector for detecting the magnitude of a specific frequency based on an output of an ionic current detector, an ionic current area calculator for calculating an ionic current area in a prescribed range during the combustion stroke of a cylinder concerned based on the output of the ionic current detector, a corrector for correcting the detected specific frequency magnitude based on the calculated ionic current area, a knock determiner for determining based on the corrected specific frequency magnitude whether the engine is knocking, and a control parameter correction amount setter for setting an amount of correction for an ignition timing control parameter based on the determination result.
U.S. Pat. No. 6,230,546 discloses a method and an apparatus for detecting knocking combustion in an internal combustion engine, by evaluating the ionic current signal sensed in the combustion chamber, is ostensibly adapted to correct or compensate the ionic current signal for longterm variations arising therein, for example due to variations in the composition of the fuel as a result of contamination with metallic components or the like.
US 20030183195 discloses an ionic current intensity determined by ionic current intensity learning means for determining the ionic current intensity based on an output from an ionic current detection circuit, at least one of a comparison reference value of a comparison reference value setting means and a control parameter correction amount of control parameter correction request amount setting means is corrected, so that, even in a case where fuel is mixed with additives, and a case where a non-standard spark plug is mounted, the ionic current amount fluctuation is accurately determined even if the amplitude of a knock signal varies due to ionic current intensity fluctuation, and correction of the comparison reference value corresponding to the ionic current intensity, or correction of the control parameter, is performed, to thereby prevent erroneous control based on erroneous knock detection, and securely achieve an excellent knock detection status and knock control status.
U.S. patent application Ser. No. 13/517,920 (PCT/SE11/50050) relates to a device for analyzing a cylinder wise performance of an internal combustion engine, comprising ion current measurement means that are arranged to measure an ion current in a engine.
These documents and their respective priority documents are incorporated by reference herein.